Diagnostic hope for killer fish disease

A unique tool for detecting the koi herpesvirus (KHV), a deadly contagious viral disease found in carp, has been launched by Cefas Technology Limited (CTL). KHV is difficult to diagnose so the new biological tests offer real peace of mind for fish farmers, wholesalers and importers who want to check that existing or potentially new stocks are KHV-free.

There is no cure and currently no vaccine for KHV, but early detection can help prevent further spread to unaffected fish stocks. The only reliable method of detecting KHV is by using state-of-the-art molecular biological techniques. CTL is the first and only company in Europe commercially providing these techniques for the diagnosis of KHV.

CTL is offering fish farmers, dealers, importers and hobbyists a polymerase chain reaction (PCR) test for either disease diagnosis or screening. Both tests can be ordered online from www.cefastechnology.co.uk, making it a simple and easy transaction.

The diagnostic test can be performed on tissue samples from clinically affected fish or fish showing signs of KHV. Live fish, whole dead fish or appropriate tissue samples can be used, with results ready within 10 days. This test is designed for 1–3 fish.

The screening test is designed to provide a disease status check to those dealing with large quantities of koi or common carp. The test can be performed on fish exhibiting no obvious symptoms of KHV and takes approximately 4 weeks to complete, including a 2-week quarantine period. This test will confirm if the KHV virus is present in the fish tested and requires either 30 or 150 fish to be supplied.

The majority of KHV outbreaks have been reported in koi carp populations at ornamental fish importers’, wholesalers’ and in hobbyists’ ponds. Extensive movements in live ornamental fish for trade and koi shows have contributed to the rapid spread of the disease around the world. KHV also poses a serious threat to wild and farmed common carp, with recent outbreaks linked to the rearing and holding of common carp alongside ornamental varieties.

Whereas the PCR tests can detect the presence of KHV, they should be used in combination with good risk management practices. These include, buying fish from a reliable supplier who can provide assurances of disease-free status, operating a period of quarantine at 21–25°C for all newly introduced stock and not mixing stock from different suppliers.

Notes to editors

1. Cefas Technology Limited (CTL) is a wholly owned subsidiary of the Centre for Environment, Fisheries & Aquaculture Science (Cefas). It offers technical and commercial solutions for specific customer needs, alongside a wide range of research and consultancy advice in fisheries and environmental management (see http://www.cefastechnology.co.uk/).  
2. Cefas is an internationally renowned scientific research and advisory establishment, based at Lowestoft since 1902. It became an executive agency of the Department for Environment, Food and Rural Affairs (formerly MAFF) in 1997. It undertakes work on fisheries management, environmental protection and aquaculture for government departments (UK and foreign, central and local), international agencies and aid organisations.  
3. The Aquaculture and Fish Health team, based at Cefas’ Weymouth laboratory, have been researching KHV and recently received funding from the English Carp Heritage Organisation (ECHO) to further this work. 
4. Carp were once a common food source in the UK and are now popular with anglers. The approximately 100,000 UK carp anglers ‘catch and return’ millions of fish every year. The carp is also the mainstay of a £3.5 billion-a-year angling industry. KHV outbreaks often cause mass mortalities resulting in considerable financial losses.
5. KHV affects koi carp (Cyprinus carpio koi), common carp (Cyprinus carpio carpio) and ghost carp (common + koi cross, Cyprinus carpio goi). It is spread from fish to fish, being highly contagious, and occurs naturally at temperatures between 15°C and 27°C.
6. Diagnosis of KHV is difficult because straightforward visual examination is unreliable (the typical symptoms are seen in a number of other carp diseases). The most prominent clinical sign is irregular discolouration of the gills that can progress to gill rot. Behavioural signs of the disease include lethargy, gasping and erratic swimming. At high water temperatures fish can die within hours of the first signs of the disease. Some fish carry KHV for long periods without exhibiting any external symptoms of the disease.  
7. The polymerase chain reaction (PCR) is a highly specific and sensitive technique in which a region of genetic material of an organism – its DNA – is replicated million-fold to produce sufficient DNA for analysis.
   • ‘polymerase’ refers to a thermal stable enzyme that replicates DNA
   • ‘chain reaction’ refers to the cyclic nature of the reaction (usually 25–40 cycles), each of which duplicates the amount of DNA product.

   Diagnostic PCR tests target DNA sequences that are unique to the organism of interest; in this case KHV, and are capable of detecting single copies of this unique sequence of DNA from a mixture of virus and normal (‘host’) DNA.  

8. Cefas scientists are available for comment; digital photos can be supplied on request.

Press contact: Anne McClarnon 01502 524370 / anne.mcclarnon@cefas.co.uk.